2,5-Furandicarboxylic acid is a furan derivative. This organic compound was first obtained by Fittig and Heinzelmann in 1876. The first review, by Henry Hill was published in 1901 (Am. Chem. Journ. 25, 439). FDCA was more than 125 years later identified by the US Department of Energy as one of 12 priority chemicals for establishing the “green” chemistry industry of the future. However, to date, no commercial process exists for its production. On the laboratory scale it is often synthesized from HMF, which in turn can be obtained from carbohydrate-containing sources such as glucose, fructose, sucrose and starch. From fructose and glucose HMF is obtained by acidic elimination of three moles of water.
The derivatives of HMF are identified as potential and versatile fuel components and precursors for the production of plastics. The polyester from 2,5-furandicarboxylic acid dimethyl ester and ethylene glycol was first reported in 1946 (GB 621,971).
WO 01/72732 describes the oxidation of HMF to FDCA. The maximum FDCA yield reported is 59%, obtained at 105° C. The oxidation of HMF in an aqueous medium with oxygen using a catalyst from the Pt-group is described in U.S. Pat. No. 4,977,283. Taarning et al. described the oxidation of HMF over gold based catalysts (ChemSusChem, 1, (2008), 75-784).
Partenheimer et al describe the synthesis of furan-2,5-dicarboxylic acid by catalytic air-oxidation of 5-hydroxymethylfurfural with the metal/bromide catalyst Co/Mn/Br in Adv. Synth. Catal. 2001, 343, pp 102-11.
In WO 2007/104514, the synthesis of ethers of HMF such as 5-methoxymethylfurfural (MMF) and 5-ethoxymethylfurfural (EMF) from biomass sources is described. Given the higher stability than HMF and hence improved production pathways and given the green reputation of these ethers, they were considered by the present inventors as interesting starting point in the preparation of furan-based monomers that could be used for the production of furandicarboxylic acid-based polyesters, for instance as an alternative for PET or FDCA-based polyamids (nylons). One of the most important conventional, oil-based, polyester monomers is Purified Terephthalic Acid (PTA) and their alkyl esters such as DiMethyl Terephthalate (DMT). The di-esters are of interest in the polymerization process, as methanol is liberated as condensation product in the reaction of DMT with a diol instead of higher boiling water that is liberated in the reaction of PTA with a diol. The lower boiling point of methanol facilitates the required removal during the polycondensation step, facilitating the formation of high molecular weight polymers.
Oxidation of the HMF ethers has not been reported. When using prior art techniques such as the above described catalyst systems, the desired FDCA could be obtained in moderate yield. Surprisingly, it was found that when using a bromide-containing cobalt and manganese-based catalyst, under specific reaction conditions, not only FDCA was obtained but that also significant amounts of esters could be obtained from direct oxidation of the ether function of HMF ethers. The FDCA+FDCA ester combined yields are with 70-85% very high. From a process point of view this is very interesting. Thus for 5-(methoxymethyl)furfural or MMF the formation of the mono methyl ester of FDCA was observed.